An Integrated Approach to Air Quality and Climate Change

Any report card on the state of the air quality in this country must contain a mix of successes, failures, and “incompletes.” Our control of many pollutants, such as carbon monoxide and lead, may earn top marks, but persistently high ozone and particulate matter levels are dragging down our GPA. While the overall trend is certainly one of improvement, with U.S emissions of harmful air pollutants cut by two-thirds since 1980, over 140 million Americans are still living in regions that violate air quality standards.

On this hypothetical report card, we would find an “Incomplete” next to the climate-warming gases, because only in recent years has the EPA begun regulating them under the Clean Air Act. Carbon dioxide and other greenhouse gases differ from “traditional” air pollutants in that they do not directly harm human health. However, the newly proposed regulations on carbon dioxide emissions from power plants could be finalized right around the time that states must develop plans for tighter ozone and particulate matter standards. This presents an opportunity to tackle three of our greatest environmental challenges in an integrated fashion, achieving better outcomes than previous pollutant-by-pollutant approaches.

Before explaining the merits of a multi-pollutant approach, we must review the successes and shortcomings of past and current policies. Roughly every five years, as epidemiology more clearly demonstrates the health impacts of air pollution, the EPA reviews each air quality standard. Individual states are then responsible for designing attainment plans, known as State Implementation Plans (SIPs). With the EPA sometimes tightening a standard before the previous goal is met, states rarely take the time to evaluate how the previous plans were working.

Our environmental research group at Rice University is aiming to fill this gap in our knowledge. In two recently published papers, which analyzed the SIPs for attaining previous standards for ozone and particulate matter, we showed that state plans were largely successful in achieving attainment by the predicted deadlines. In fact, when predictions were slightly inaccurate, it was more often due to underestimations of the benefits of air pollution control, rather than falsely promised success. Overall, Rice group’s analyses indicate that the complex models used to predict air quality improvements are working adequately, and that states are not being overly optimistic in their predictions.

Still, the SIPs were not without their shortcomings. First off, both states and the EPA tend to focus on one pollutant at a time, despite the interrelated chemistry that leads to the formation of ozone and particulate matter. The setting of air quality standards and development of states plans occur on separate timelines, which impedes the design of control measures that could potentially curb both pollutant levels simultaneously.

Secondly, the EPA sets National Air Quality Standards (NAAQS) based on health effects of the pollutant, but states design SIPs primarily based around cost and efficacy of attaining these standards. Therefore, it is not clear that the strategies for achieving attainment necessary have the maximum public health benefits.

Integration of ozone and particulate matter regulations should be a logical step towards a multi-pollutant approach. Integration of CO2 policy, on the other hand, could be a wider gap to bridge. The Rice analyses addressed state plans for air pollutants, but states have never before been mandated to reduce greenhouse gas emissions. Because the EPA’s proposed Clean Power plan requires statewide reductions in power sector CO2, versus the regional plans for air pollutants, and due to the different deadlines for each pollutant, there will be a tendency to view the rules in isolation.

However, there are clear solutions that would simultaneously cut CO2 and ambient air pollution. Achieving carbon caps using efficiency and renewable energy will simultaneously cut all primary and secondary emission products of power plants, including PM and ozone. In contrast, pursuing carbon sequestration technology, which requires massive amounts of energy, would result in higher consumption of fossil fuels and thus higher pollutant emissions, other than the captured CO2. Likewise, some approaches to cleaning PM and ozone air pollution can also help cool the planet, while other approaches are less favorable for climate.

Air quality in the United States may be substantially cleaner today than 30 years ago, but stubbornly high ozone and particulate matter levels indicate that ongoing improvements are needed. Jointly considering air quality and climate offers the best opportunity to achieve win-win solutions that better protect our health, while also beginning to achieve the greenhouse gas reductions needed to combat climate change.

Amanda MacDonald is a junior at Rice University, majoring in Civil and Environmental Engineering. This past summer she worked with the Cohan Research Group at Rice, which focuses on atmospheric processes and air quality management. She is especially interested in the United States' transition to clean energy.